Normally you count them and get half of the shot ones back. It sucks. Thats why almost nobody does it.

Technically no. In reality, yes. Bows require arrows and most spells require a material component. These are never tracked unless it's something special. If a spell costs thousands of gold in material components to cast, it should be required that you actually aquire that component, but otherwise pretty much everyone just assumes that you are prepared with a enough basic materials. The same for arrows and any other basic resources usually. I've never played with a party that tracks food and water, for example. It's just assumed you've come prepared.